AtkValue: refactoring AtkValue

In summary:
  * Stop to use GValue to get/set the value and use doubles instead
  * Include the support for a string description and subranges

https://bugzilla.gnome.org/show_bug.cgi?id=684576
AtkValue: add a testvalue example, with a small AtkValue
 implementation

https://bugzilla.gnome.org/show_bug.cgi?id=684576
atkvalue: add strings to translate value type names
Updated Norwegian bokmål translation
Updated POTFILES.in
Updated Polish translation
Updated Brazilian Portuguese translation
Updated Galician translations
Add translations notes to atkvalue.c
Updated Hungarian translation
Updated Korean translation
Updated Spanish translation